1. Field of the Invention
The present invention relates to an optical writing device, an image forming apparatus, and a method of controlling an optical writing device.
2. Description of the Related Art
There has been a growing trend in recent years to computerize information. This trend makes an image processing apparatus, such as a printer and a facsimile used to output computerized information and a scanner used to computerize a document, indispensable equipment. Such an image processing apparatus often has an image capturing function, an image forming function, a communication function, and the like so as to be configured as a multifunction peripheral operable as a printer, a facsimile, a scanner and a copier.
An electrophotographic image forming apparatus is widely used as an image forming apparatus, which is one type of such an image processing apparatus, for use in outputting a computerized document. An electrophotographic image forming apparatus produces a printout by exposing a photosensitive element to light to thereby form an electrostatic latent image, forming a toner image by developing the electrostatic latent image with a developer such as toner, and transferring the toner image onto paper.
A method of performing exposure of a photosensitive element by an optical writing device included in an electrophotographic image forming apparatus includes a laser diode (LD) raster optical system method and a light emitting diode (LED) writing method. When an optical writing device uses the LED writing method, the optical writing device includes an LED array (LEDA) head on which LEDs each associated with one of pixels of one main scanning line are arranged in an array.
An electrophotographic optical writing device generally performs a neutralization process each time one print job is completed. The neutralization process makes a charged state of a photosensitive element at the time of starting a next print job uniform so that unevenness in amount of toner clinging to the photosensitive element is suppressed to maintain image quality (see Japanese Patent Application Laid-open No. 8-234646, for example).
Conventionally, an optical writing device that uses the LD raster optical system has been mainstream. When the LD raster optical system is used, exposure of an entire surface of a photosensitive element can be performed by keeping an LD light source lit; in this case, maximum electric current is unaffected. In contrast, when the LED writing method is used, it is necessary to cause all LEDs contained in an LEDA head to emit light to perform exposure of an entire surface of a photosensitive element.
Total light quantity for use in optical writing using an LED head is regulated, and control is performed in normal writing control so as to prevent a situation where all LEDs on one main scanning line light up concurrently. Therefore, an amount of electric current necessary for the normal writing control is smaller than an amount of electric current that flows to cause all the LEDs contained in the LED head to emit light. However, to perform a neutralization process as described above, a power source unit and a circuit of a capacity appropriate for an amount of electric current that is not necessary for the normal writing control become necessary because the neutralization process involves lighting up all the LEDs. This not only increases apparatus costs but also makes an apparatus configuration inefficient.
The problem described above is not a problem of only an optical writing device that uses an LED head but can be a problem of any optical writing device that performs exposure of a photosensitive element using a light-source element array made up of a plurality of light-source elements as well.
There is a need to reduce a maximum amount of electric current necessary for a neutralization process in an optical writing device that performs exposure of photosensitive elements using light-source element arrays each made up of a plurality of light-source elements.